The invention is a method of selective etching and a waveguide produced by said method.
The chemical cutting of metal pieces is known. Chemical cutting consists in the ablation of certain parts of a piece of metal by chemical etching. The piece of metal may be a copper sheet. The chemical reagent may be sulfuric acid, nitric acid, iron perchloride. Chemical cutting has the advantage of inducing no stress in the piece cut as opposed to mechanical machining. In addition, every cut is made during a single pass in the chemical cutting machine independently of the complexity of the pattern.
The sheet to be cut out is itself protected by a layer chemically insensitive to the reagent. The protective layer is absent only above the parts of the sheet to be ablated.
Chemical cutting has the great drawback of only allowing flat pieces to be produced.
The method of the present invention provides chemical etching of a metal sheet ensuring local reduction of the thickness of the metal. For example, half of the thickness of the sheet is removed locally. Thus, grooves may be formed for very accurate bending of the sheet. Furthermore, by locally removing half of the thickness of the metal sheet, it is possible to form a rabbet for closing a developable volume from a flat sheet. The rabbet also allows large dimensioned objects to be formed by assembling together sheets of smaller size. Thus the method of the invention is applied to the construction of waveguides, particularly trough guides or comb guides as well as features to locally perturb an electromagnetic field.
The principal object of the invention is a method for the chemical ablation of material from a metal sheet covered on both its faces with a protective film comprising patterns symmetrical with respect to the plane of the sheet leaving the sheet bare at desired positions, said protective films further comprising patterns leaving the metal sheet bare on one of its faces, the other face of the sheet being protected at this position by the protective film.